cpbackup looks at the timestamps of the backup archives. A daily backup will not be made again until the existing daily archives are 24 hours old. Likewise, weekly backups need to be 7 days old, and so on. After running a manual backup, it is best to avoid running any new manual backups in order to let the automatic backup "catch up" with the timestamps, i.e. let the timestamps age so that backups will again be done automatically.